The Influence of Plasticity on Crack Length Measurements Using the Potential Drop Technique

The potential drop (PD) technique is one of the most common methods for determining crack growth however, other factors can also change the resistance of the specimen, which may erroneously be interpreted as crack extension. In tough, ductile materials, plastic strain can cause a significant change in PD. This paper presents an experimental investigation which quantifies the apparent crack extension due to strain, prior to the onset of physical crack growth and considers ways to mitigate it. Compact Tension, C(T), and Single Edge Notch Tension, SEN(T), specimen geometries are considered with a range of crack lengths. The influence of probe location is also considered.

The results identify apparent crack extensions of up to 1.0 mm in the absence of any physical crack extension. This can be reduced through careful selection of probe locations. Appropriate locations are suggested for the geometries considered. It is also shown that high constraint geometry can significantly reduce the influence of plasticity on PD.